1. Field of the Invention
The present invention relates to a latex obtainable by reaction in a gradient regime in which the initial molar ratio of the entering components is adjusted to a target molar ratio through at least one discontinuous change in the amount fed in per unit time.
2. Discussion of the Background
Emulsion polymerization conducted with monomer mixtures which are capable of side reactions (e.g., Diels-Alder reaction) yield side-products which occur as accompaniments in the latex. Since these substances have a strong intrinsic odor, efforts have been made to minimize the amount of these side-products.
U.S. Pat. No. 3,804,881 discloses emulsion polymerization with a permanently varying monomer ratio of the entering polymerizing components. In that process the variation in the amount added per unit time is kept permanently constant. A disadvantage of the process is that during the polymerization large amounts of by-products, especially Diels-Alder products, are formed. No specific methods are indicated for reducing the level of accompaniments.
EP 0 853 636 B1 describes emulsion polymerization using a seed latex, performed by the feed technique, with a continuous variation of the monomer ratio of the entering polymerizing components. In that case, the variations in the amount added per unit time are kept constant throughout the metering time of the two monomer mixtures. A disadvantage of the process is that during the polymerization large amounts of by-products, especially Diels-Alder products are formed. No specific methods are indicated for reducing the level of accompaniments.